Calcium phosphates, in particular calcium hydroxyapatite (Ca5(PO4)3OH) and other hydroxyapatite materials, are known for use as skeletal reconstitution materials. Various hydroxyapatite materials are disclosed for example in U.S. Pat. Nos. 4,861,733, 6,024,985, 6,387,414, 6,426,114, 6,582,672, 6,585,946 and 6,596,338.
Silicon substituted hydroxyapatite and tricalcium phosphate materials are also known. Ruys et al., 1993 (Silicon-Doped Hydroxyapatite, J. Aust. Ceram. Soc. 29(1/2) pp 71-80) discloses a silicon substituted hydroxyapatite material. Kim et al., 2003 (Biomaterials, 24, 1389-98) discloses a silicon and magnesium substituted hydroxyapatite material. Bonfield et al., 1999 (J. Biomed Mater Res. March 15; 44(4):422-8) discloses a silicon-substituted hydroxyapatite prepared by a precipitation technique. Sayer et al., 2003 (Structure and composition of silicon-stabilized tricalcium phosphate, Biomaterials, 24; 369-382) discloses a silicon-stabilized tricalcium phosphate material for use in skeletal tissue repair. U.S. Pat. No. 6,312,468 discloses a silicon-substituted apatite that can be converted upon heating to a silicon-substituted hydroxyapatite comprising between 0.1% to 5% by weight of silicon for use as a synthetic bone material. The silicon-substituted hydroxyapatite is stated to be free of calcium oxide and/or tricalcium phosphate.
Oxyapatites are also known and often used in restorative materials for orthopedic and dental applications.
The Applicant has now identified a novel compound, silicon substituted oxyapatite (Si-OAp) that has wide use as a synthetic bone biomaterial compound in a variety of orthopedic applications such as skeletal implants.